Allen key in L-shape with a tip size of 1. A hex key is ideal for all types of use by any professional engineer, plumber, carpenter, electrician, as well as for household use. Hex keys are formed from a single piece of hexagonal rod made of hard steel with blunt ends that fit comfortably into similarly shaped screw slots. It is bent at 90 degrees, forming two arms of unequal length that resemble the Latin letter "L".